When the levee breaks, this is the result.
When the levee breaks, this is the result. Cath Adams

Will mega channel to flood proof Lismore actually work?

A PROPOSED $90 to $120 million mega-channel to flood proof Lismore could be a dud, with recent modelling revealing it might only reduce a major flood in Lismore by up to 40cm.

But the conclusions remain mired in controversy.

The mega channel had been floated as an idea for several years as a way to get floodwater from Leycester Creek to bypass the Lismore CBD.

The canal would divert much of the excess water on the western arm of the down the so-called "airport floodway", west of South Lismore and end up coming out at Loftville, south of Lismore.

But regional water authority Rous County Council recently ran flood models to test the proposal, and found the 300m wide channel might not be worth the money.

Rous County Council manager for planning and delivery Michael McKenzie said the canal would have reduced CBD flooding by up to 400mm, which is not enough to stop a major flood from overtopping the levee.

"What we found is while it provided Lismore a benefit, espeically in that South Lismore area, it didn't solve any flooding of the CBD," Mr McKenzie said.

Its effect was limited because of downstream "flood control points" - or pinch points, such as Sandy Point - which can hold up the flow of water or even reverse it in major floods.

However, an accomplished civil engineer who took the original proposal to Rous County Council believes the water authority's flood model isn't good enough to adequately test the idea.

Peter Thorpe grew up in South Lismore and went on to have a 50 year career in engineering, including running his own firm for more than two decades delivering major civil construction projects.

Working out ways of flood proofing Lismore has been one of his lifelong passions.

He initially costed the airport channel at $50 million, not $120 million.

"I don't claim to be an expert in modelling but I have run a medium-sized civil construction company with a turnover of $50 million a year in a very competitive environment, so I'm happy to stick to my guns in terms of the estimate of the cost, and we haven't seen the basis of Rous's figures," he said.

But Mr Thorpe also believes Rous County Council's conclusions on the channels effect aren't based on a robust flood model.

"I'm suggesting a body which has sufficient experience in this area undertake what work needs to be done and the obvious choice is the Public Works department."

In fact, Rous County Council is currently "rigorously assessing" tenders for a new, improved Lismore flood model, as the effort to find the best flood mitigation strategy continues.

Mr McKenzie said while the current model was "quite robust" it had "limitations" and wasn't in line with current Australian best practice.

"It's quite a complex set of modelling scenarios, you have the confluence of two rivers... consequentially modelling is quite a challenge."

The new flood model is expected to be ready within six months.

Meanwhile, a less ambitious $12 million proposal to remove viaducts and railway lines parallel to Kyogle Rd and conduct earthmoving between Caniaba Rd and Three Chain Rd is expected to deliver 20-30cm lower floods in some areas.

Nationals candidate for Lismore Austin Curtin has launched a community petition to campaign for funding for the project from the NSW Government.

It would work in a similar fashion to the grand channel, but on a smaller scale.

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